Wireless devices typically operate in one or more cellular communication standards and/or wireless connectivity standards, each standard being allocated in one or more frequency bands, and said frequency bands being contained within one or more regions of the electromagnetic spectrum.
For that purpose, a space within the wireless handheld or portable device is usually dedicated to the integration of a radiating system. The radiating system is, however, expected to be small in order to occupy as little space as possible within the device, which then allows for smaller devices, or for the addition of more specific equipment and functionality into the device.
This is even more critical in the case in which the wireless device is a multifunctional wireless device. Commonly-owned patent applications WO2008/009391 and US2008/0018543 describe a multifunctional wireless device. The entire disclosure of said application numbers WO2008/009391 and US2008/0018543 are hereby incorporated by reference.
A typical wireless device must include a radiating system capable of operating in one or more frequency regions with good radio-electric performance (such as for example in terms of input impedance level, impedance bandwidth, gain, efficiency, or radiation pattern). Moreover, the possibility to operate in several frequency regions allows global connectivity, increased connectivity speeds, or multiple functionalities.
For a good wireless connection, high gain and efficiency are further required. Other more common design demands for radiating systems are the voltage standing wave ratio (VSWR) and the impedance which is supposed to be about 50 ohms. Other demands for radiating systems for wireless handheld or portable devices are low cost and a low specific absorption rate (SAR).
A radiating system for a wireless device typically includes a radiating structure comprising an antenna element which operates in combination with a ground plane layer providing a determined radio-electric performance in one or more frequency regions of the electromagnetic spectrum. This is illustrated in FIG. 1, in which it is shown a radiating structure 100 comprising an antenna element 101 and a ground plane layer 102. Typically, the antenna element has a dimension close to an integer multiple of a quarter of the wavelength at a frequency of operation of the radiating structure, so that the antenna element is at resonance at said frequency and a radiation mode is excited on said antenna element.
A problem associated to the antenna element in a wireless device is that the volume dedicated for such integration has continuously shrunk with the appearance of new smaller and/or thinner form factors for wireless devices, and with the increasing convergence of different functionality in a same wireless device.
Some techniques to miniaturize and/or optimize the multiband behavior of an antenna element have been described in the prior art. However, the radiating structures therein described still rely on exciting a radiation mode on the antenna element.
For example, commonly-owned co-pending patent application US2007/0152886 describes a new family of antennas based on the geometry of space-filling curves. Also, commonly-owned co-pending patent application US2008/0042909 relates to a new family of antennas, referred to as multilevel antennas, formed by an electromagnetic grouping of similar geometrical elements. The entire disclosures of the aforesaid application numbers US2007/0152886 and US2008/0042909 are hereby incorporated by reference.
Some other attempts have focused on antenna elements not requiring a complex geometry while still providing some degree of miniaturization by using an antenna element that is not resonant in the one or more frequency ranges of operation of the wireless device.
For example, WO2007/128340 discloses a wireless portable device comprising a non-resonant antenna element for receiving broadcast signals (such as, for instance, DVB-H, DMB, T-DMB or FM). The wireless portable device further comprises a ground plane layer that is used in combination with said antenna element. Although the antenna element has a first resonance frequency above the frequency range of operation of the wireless device, the antenna element is still the main responsible for the radiation process and for the electromagnetic performance of the wireless device. This is clear from the fact that no radiation mode can be excited on the ground plane layer because the ground plane layer is electrically short at the frequencies of operation (i.e., its dimensions are much smaller than the wavelength).
With such limitations, while the performance of the wireless portable device may be sufficient for reception of electromagnetic wave signals (such as those of a broadcast service), the antenna element could not provide an adequate performance (for example, in terms of input return losses or gain) for a cellular communication standard requiring also the transmission of electromagnetic wave signals.
Commonly-owned patent application WO2008/119699 describes a wireless handheld or portable device comprising a radiating system capable of operating in two frequency regions. The radiating system comprises an antenna element having a resonance frequency outside said two frequency regions, and a ground plane layer. In this wireless device, while the ground plane layer contributes to enhance the electromagnetic performance of the radiating system in the two frequency regions of operation, it is still necessary to excite a radiation mode on the antenna element. In fact, the radiating system relies on the relationship between a resonance frequency of the antenna element and a resonance frequency of the ground plane layer in order for the radiating system to operate properly in said two frequency regions.
The entire disclosure of the aforesaid application number WO2008/119699 is hereby incorporated by reference.
Some further techniques to enhance the behavior of an antenna element relate to optimizing the geometry of a ground plane layer associated to said antenna element. For example, commonly-owned co-pending patent application U.S. Ser. No. 12/033,446 describes a new family of ground plane layers based on the geometry of multilevel structures and/or space-filling curves. The entire disclosure of the aforesaid application number U.S. Ser. No. 12/033,446 is hereby incorporated by reference.
In order to reduce as much as possible the volume occupied into the wireless handheld or portable device, recent trends in handset antenna design are oriented to maximize the contribution of the ground plane to the radiation process by using non-resonant elements.
Commonly owned patent applications, WO2010/015365 and WO2010/015364, the entire disclosures of which are hereby incorporated by reference, are intended for solving some of the aforementioned drawbacks. Namely, they describe a wireless handheld or portable device comprising a radiating system including a radiating structure and a radiofrequency system. The radiating structure is formed by a ground plane layer and at least one radiation booster. The radiation booster is not resonant in any of the frequency regions of operation and consequently a radiofrequency system is used to properly match the radiating structure to the desired frequency band/s of operation.
More particularly, in WO2010/015364 each radiation booster is intended for providing operation in a particular frequency region. Thus, the radiofrequency system is designed in such a way that the first internal port associated to the first radiation booster is highly isolated from the second internal port associated to a second radiation booster due to the distance in terms of wavelength between the internal ports of the radiating structure and therefore, between the radiation boosters.
Another technique is disclosed in U.S. Pat. No. 7,274,340, which shows a radiating system based on the use of two non-resonant elements providing impedance matching through the addition of two matching network systems. The two non-resonant elements are arranged in such a manner that they provide coupling to the ground plane. Despite the use of two non-resonant elements, the size of the element for the low band is significantly large, being 1/9.3 times the free-space wavelength of the lowest frequency for the low frequency band. Due to such size, the low band element would be a resonant element at the high band. The size of the low band element undesirably contributes to increase the printed circuit board (PCB) space required by the antenna module. In fact, such radiating system is still about the size of a conventional internal antenna inside a handset, therefore the overall radiating system does not provide a significant space advantage compared to the existing alternative solutions.
Therefore, a wireless device not requiring a large antenna element and only requiring a minimum area in the PCB would be advantageous as it would ease the integration of the radiating structure within the wireless device.
A wireless device that comprises a concentrated configuration of radiation booster/s, yet the wireless device featuring an adequate radio-electric performance in two or more frequency regions of the electromagnetic spectrum would be an advantageous solution. This problem is solved by a concentrated wireless device according to the present invention.